The present invention relates to stents for angioplasty. In particular, the invention relates to a stent having a cellular design.
The term xe2x80x9cstentxe2x80x9d is intended to indicate devices useful for endoluminal insertion (for example, in a blood vessel), usually effected by means of catheterization, with subsequent deployment in place so as to achieve local support of the lumen. The primary purpose of the stent is to eliminate and avoid the restenosis (i.e., narrowing or closure) of the treated area.
For a general review of vascular stents, reference is made to xe2x80x9cTextbook of Interventional Cardiologyxe2x80x9d edited by Eric J Topol, W.B. Saunders Company, 1994 and, in particular, to section IV of volume II, entitled xe2x80x9cCoronary Stentingxe2x80x9d.
Many patents also provide a general review of stents, for example, U.S. Pat. Nos. 4,503,569; 4,768,507; 4,776,337; 4,800,882; 4,830,003; 4,856,516; 4,886,062; 4,907,336; and EP 0 201 466A.
Notwithstanding the extensive research and experimentation in the stent field, as documented in the patent literature, only a relatively small number of operative solutions have, until now, found practical application. This is due to various factors, which include the following problems or requirements:
while moving toward the treatment site, the stent should be capable of adapting to the path, which may include various curved sections;
distortion of the stent while it is being positioned should not be detrimental to the ability of the stent to provide an effective support when it is positioned and deployed;
the longitudinal shortening effect which occurs in many stents upon deployment should be limited, if not avoided;
maximum homogeneity and uniformity in the expansion of the stent should be achieved at the desired location;
an extensive support surface should be provided to the wall of the lumen which is being supported;
the origination of complex shapes and/or possible stagnation sites, especially in blood vessels, should be avoided, in order to avoid undesirable phenomena such as coagulation or thrombosis; and
the stents should be able to be simply and reliably produced using available technology and they should incorporate the requirements listed above.
A stent is subject to various forces, including compression, flexure, and torsion. These stresses often cause the stent to perform in an undesirable manner. Additionally, a significant disadvantage of current stent designs is their failure to distribute these stresses throughout the structure of the stent. Each of these stresses is maximized in a particular area of the stent. In current stent designs two or more of these areas of maximum stress overlap. This results in at least two problems. First, an overlap of the maximum stress areas may overly fatigue the stent and cause failure in an area of overlapped maximum stress. Second, the failure to distribute or discharge the maximum stress of these forces at different areas causes stress concentration on the vessel wall which may cause vessel wall injury. Thus what is needed in the art is a stent meeting the requirements listed above that will avoid stress concentration and elastic distortion as well as provide good elastic matching between the stent and the vessel into which it is placed.
This invention is a stent having a substantially tubular body defining a longitudinal axis comprising first and second adjacent annular segments, each segment defining a substantially sinusoidal shape having a plurality of peaks and valleys, the peaks of the first segment extending toward the second segment and being aligned longitudinally with the valleys of the second segment; a plurality of bridge elements having a U-shaped portion between first and second connector arms, the first connector arm of one bridge element being connected between a first peak and a first valley of the first segment and the second connector arm being connected between a first peak and a first valley of the second segment in a manner such that the U-shaped portion extends in the direction of the first peak of the first segment and the first valley of the second segment.
The U-shaped portion of the plurality of bridge elements may be oriented in the same direction. Alternately, they may be oriented in one direction between one pair of adjacent annular segments, and in the opposite direction between another pair of adjacent annular segments. Preferably, the connector arm of the bridge element joins the annular segment at the zero point of the sinusoidal wave shape. In one embodiment, each connector arm joins each annular segment at zero points of the sinusoidal wave separated by 360xc2x0. Alternately, the connector arms may join zero points separated by 360xc2x0 between one pair of adjacent segments, and zero points separated by 720xc2x0 between another pair of adjacent segments.
In a second aspect, this invention is a method of preventing restenosis by providing the stent described above and deploying it within a body lumen.
In a third aspect, this invention is a method of making a stent by providing a tubular blank and forming the tubular blank into a stent having the geometry described above.
In a further aspect this invention is a stent having a substantially tubular body defining a longitudinal axis. The stent comprises first and second adjacent annular segments, each segment having a substantially sinusoidal wave shape. The stent further includes first and second bridge elements, the first bridge element having a first end connected to the first annular segment at a zero point of the sinusoidal wave shape and having a second end connected to the second annular segment at a zero point of the sinusoidal wave shape. The second bridge element has a first end connected to the first annular segment at a zero point of the sinusoidal wave shape spaced 360xc2x0 from the connection of the first bridge element to the first annular segment and a second end connected to the second annular segment at a zero point of the sinusoidal wave shape 360xc2x0 from the connection of the first bridge element to the second segment, the first and second bridge elements and a portion of the first and second annular segments between the connection points of the bridge elements together defining a cell.
In a further aspect, the invention is a stent having a substantially tubular body defining a longitudinal axis and having a plurality of annular segments, each segment having a substantially sinusoidal wave shape. The stent includes a plurality of bridge elements, each bridge element having a first end connected to one annular segment at a zero point of the sinusoidal wave shape and a second end connected to an annular segment adjacent to the one annular segment at a zero point of the sinusoidal wave shape of the adjacent annular segment, the annular segments and bridge elements being configured such that when compression, flexure and torsion forces are applied to the stent they generate first maximum stress regions, second maximum stress regions, and third maximum stress regions, where the first, second and third maximum stress regions do not overlap.